Search Results (1,551)

Rock cohesion ($c$) and angle of internal friction ($\phi$) are core parameters for rock mass stability analysis and engineering design; however, traditional triaxial tests are costly and time-consuming, limiting their availability in preliminary engineering assessments. To address this limitation, this study develops a machine learning framework that predicts these parameters from easily measurable physical properties, enabling rapid and cost-effective estimation without the need for complex laboratory testing. Based on a total of 199 sets of measured data from four rock types (shale, limestone, quartzite, and quartz-mica schist) in the Himalayan region, this study uses P-wave velocity ($V_p$), density ($\rho$), uniaxial compressive strength (UCS), and tensile strength (TS) as input variables. It employs four models: Support Vector Regression (SVR), Random Forest (RF), Multi-Layer Perceptron (MLP), and extreme gradient boosting (XGBoost) to predict $c$ and $\phi$. Hyperparameters were tuned using grid search and Bayesian optimization. We compared unified modeling with rock-type-specific modeling, performed interpretability analysis using SHapley Additive exPlanations (SHAP), and tested robustness by introducing Gaussian noise. The results show that XGBoost produced the best predictions at$c$ (test set $R^2$ = 0.9901, RMSE = 0.512 MPa), while the Bayesian-optimized SVR model yielded the best results at $\phi$ ($R^2$ = 0.9776, RMSE = 0.744°). Rock-type-specific modeling improved the $R^2$ for limestone at $\phi$ by 0.3541; the SHAP contribution for UCS and TS exceeded 70%; Random Forest demonstrated the best noise resistance, with a decrease in $R^2$ of less than 0.04 under 10% noise. In summary, the strategy proposed in this paper allows for the selection of prediction schemes based on data quality and lithological differences, providing a feasible approach for rapidly obtaining rock strength parameters. Full article

This study evaluates the effectiveness of water-soluble epoxy resin for stabilising clay soils in the design of column-type reinforcement in soft ground. To evaluate the influence of varying mix proportions of epoxy resin on the strength of a stabilised silty clay soil, specimens were subjected to a series of unconfined compression tests at various curing ages. In addition, undrained unconsolidated, isotropically consolidated undrained, and isotropically consolidated drained triaxial tests were conducted on specimens after 180 days of curing. Finally, the dynamic behaviour of the treated soil was investigated via isotropically consolidated undrained cyclic triaxial testing. Furthermore, the effect of incorporating epoxy resin on the key physical properties was assessed via water permeability, porosity, and viscosity measurements. The experiments showed that the use of this resinous material resulted in an appreciable increase in all strength values. Moreover, all stabilised specimens exhibited a substantial improvement in cyclic properties, with failure occurring at significantly elevated stress levels and after enduring a larger number of loading cycles, compared to their untreated counterparts. The laboratory results presented here offer critical guidelines for future experimental studies aimed at improving the efficacy of this material in the chemical treatment of weak soils and deep soil mixing applications. Full article

Reservoir landslides pose a persistent threat to the safe operation of hydropower projects, particularly where altered rock masses within water-level fluctuation zones undergo repeated wetting–drying and seepage-induced deterioration. This study investigates the mechanical behavior and long-term strength evolution of altered granite from the Guobu Slope near the Laxiwa Arch Dam in Qinghai, China. Rock masses with four alteration degrees, ranging from complete to slight alteration, were examined through an integrated experimental program involving torsional shear tests, hydro-mechanical coupled triaxial tests, large-scale direct shear and ring shear tests, Brazilian splitting tests, and long-term P-wave velocity monitoring. The results demonstrate that increasing water content progressively weakens the shear strength of altered granite, while elevated seepage pressure further reduces its strength and deformation resistance under hydro-mechanical coupling. Residual shear behavior also shows a clear dependence on water content, indicating that post-peak strength deterioration should be considered in slope stability assessment. Long-term P-wave monitoring further reveals that mechanical degradation is more pronounced during the early stage and gradually approaches a relatively stable state, suggesting a site-specific decelerating deterioration process rather than unlimited strength loss. Based on the experimental results, empirical relationships between shear-strength parameters and water content are established, and long-term lower-bound strength parameters are proposed for altered granite with different degrees of alteration. These findings provide experimental support for understanding the hydro-mechanical deterioration and long-term deformation behavior of reservoir-bank altered rock masses and offer a basis for parameter selection and stability assessment when combined with rock-mass reduction, field calibration, and sensitivity analysis. Full article

Large-scale and long-term hydrogen storage is a key requirement for a sustainable hydrogen-based energy system. Although underground hydrogen storage (UHS) in porous media has gained increasing attention, the behavior of hydrogen during cyclic injection and withdrawal remains poorly understood. This study experimentally investigates the effects of cyclic hydrogen injection cycles (3, 6, 9, and 12 cycles) on the physical and mechanical properties of both dry and brine-saturated Berea, which serves as a representative reservoir rock. Porosity, permeability, and mineral composition of the samples were measured before and after the injection cycles, while triaxial tests were conducted post-injection and compared with reference sister samples. Results show negligible and inconsistent mineralogical changes before and after hydrogen injection. Porosity remained nearly constant (<2 percentage variation), whereas permeability declined by more than 20% in samples, which can impact recovery efficiency. Mechanical properties remained largely unchanged, indicating stability. However, further experimental and modeling studies are required to better understand the observed permeability reduction and its implications for underground hydrogen storage (UHS). Full article

Tight reservoirs commonly exhibit low permeability and pronounced lithological heterogeneity, resulting in complex interactions among far-field stress, local structural weakness, and fluid-driven fracture propagation. In this study, four non-replicated 2 m × 2 m × 1 m physical-model specimens representing tight glutenite, tight sandstone, and No. 3 coal rock from the Huabei Oilfield were investigated using an ultra-large true-triaxial hydraulic-fracturing system. Surface-fracture observations, microseismic monitoring, and high-frequency wellhead-pressure measurements were integrated to compare fracture responses under lithology-specific combinations of injection rate, fluid viscosity, perforation configuration, and stress state. The tested glutenite cases exhibited branched or localized fracture patterns depending on the combined treatment configuration; the sandstone case was dominated by a throughgoing main fracture approximately aligned with the principal-stress direction; and the coal-rock case showed extensive participation of bedding and cleat systems. These morphological differences were accompanied by distinct pressure and microseismic signatures, indicating different pathways of hydraulic-energy redistribution and fracture activation. For the two glutenite cases, the combined change from a single-perforation configuration at 0.5 m³/min to three helical perforations at 120° and 0.7 m³/min was associated with a 42.2% larger microseismic-derived stimulated reservoir volume (SRV). Taken together, these responses indicate a shift from stronger far-field-stress-controlled localization in the comparatively uniform sandstone to progressively greater local structural control by heterogeneous interfaces in glutenite and by bedding/cleat discontinuities in coal rock. Because each configuration was represented by a single specimen and several experimental variables changed simultaneously among cases, the observed differences are interpreted as case-specific mechanistic trends rather than statistically established universal relationships. The results show the value of combining fracture morphology, microseismic spatial evolution, and pressure dynamics for interpreting lithology-dependent fracture propagation in ultra-large physical models and for developing qualitative, lithology-adapted hydraulic-fracturing concepts. Full article

Numerical modelling is a powerful tool used in geomechanics; however, its reliability depends on proper validation. This study demonstrates the use of intelligent rock bolt measurements to validate the numerical model of underground deformation, providing a practical and applicable approach even with all numerical modelling simplifications. A numerical model of a selected Case Study Location was developed using geomechanical data from laboratory tests (uniaxial compressive strength, triaxial test, and Brazilian test). The numerical model was validated using deformation data collected by intelligent rock bolts installed in the underground mine. Applying statistical data correction methods, the model data accuracy was further improved. Applying Kalman filtering improved the correlation between measured and modelled deformations from 0.90 to 0.98, demonstrating the effectiveness of statistical methods. The novelty of this work lies in the combined use of intelligent rock bolts, FEM simulations, and statistical data correction to achieve a practical and reproducible validation framework, even when simplified geological assumptions are used. Full article

Understanding the failure mechanism of soft rock roadways in high-humidity environments, as well as designing appropriate control measures, are critical for ensuring their stability. In this study, swelling and triaxial compression tests on argillaceous sandstone were first performed. Results show that the triaxial compressive strength (TCS), elastic modulus, cohesion, and internal friction angle of argillaceous sandstone are all decreased due to the water weakening effect. Then, a self-developed finite-element-based numerical code was employed to elucidate the role of humidity diffusion in the deformation and failure of soft rock roadways. Simulation results indicate that under the influence of humidity, high stress concentration zones develop, initiating microcracks within these regions. As humidity continues to diffuse, the high stress concentration zones expand and migrate deeper into the surrounding rock, causing microcracks to propagate and accelerating humidity diffusion. This cyclical process repeats, ultimately resulting in macroscopic fracturing. The failure of roadway exhibits a tensile–shear mixed mode during humidity diffusion. A comparative analysis of four control measures reveals that conventional non-waterproof shotcrete primary support is of limited effectiveness in ensuring the stability of high-humidity soft rock roadways. It is essential to promptly establish a closed waterproof support structure. Furthermore, localized support defects significantly impact control effectiveness. Full article

Thin spray-on liner (TSL) technology provides rapid and highly automated surface support for underground coal mine roadways. However, in deep roadways affected by high in situ stress, mining-induced disturbances, and fractured surrounding rock, conventional TSL materials require improved tensile–shear resistance, deformation compatibility, and support adaptability. Although fiber reinforcement is an effective method for enhancing polymer composites, systematic studies on the effects of fiber type and dosage in reactive polymer-based TSL materials remain limited. In this study, a commercially available two-component polyurea-silicate-based TSL matrix was reinforced with polyvinyl alcohol (PVA) fibers, polypropylene mesh fibers, and toughened polypropylene fibers at volume fractions of 0.25–1.50%. A stepwise experimental program, including uniaxial compression, variable-angle shear, tensile, circular-indenter buffered shear, and true triaxial tests, was conducted to evaluate the mechanical behavior and support-related performance of the fiber-reinforced TSL materials. The basic mechanical tests showed that the 0.75% toughened polypropylene fiber group maintained favorable compressive and shear resistance, achieving a cohesion of 8.65 MPa and an internal friction angle of 24.12°. PVA fibers exhibited higher tensile reinforcement efficiency at relatively low contents, with the 0.25% PVA fiber group reaching a peak tensile stress of 13.61 ± 1.00 MPa. The 1.0% PVA fiber group showed good deformation coordination, with a compressive strength of approximately 49.87 MPa. In the circular-indenter buffered shear test, the 1.0% PVA fiber group reached a peak load of 0.636 ± 0.055 kN and an absorbed energy of 3.118 ± 0.832 J at 10 mm displacement. Under true triaxial loading, the 1.0% PVA fiber group absorbed 311.4 J of energy at a displacement of 10 mm, approximately 5.5% higher than that of the 0.75% toughened polypropylene fiber group. Therefore, 1.0% PVA fiber reinforcement is recommended as the optimal reinforcement scheme for polymer-based TSL materials used in deep, fractured, and large-deformation coal mine roadways. Full article

Natural-fracture connectivity substantially influences hydraulic-fracture interaction with pre-existing discontinuities, but its quantitative role in fracture-network propagation remains insufficiently constrained. In this study, a coupled LEFM–cohesive-zone hydraulic-fracture propagation model was developed by combining crack-tip deflection criteria, traction-separation damage evolution and fluid–solid coupling. True triaxial hydraulic-fracturing experiments were conducted on artificial fracture networks with I-, V-, Y- and X-shaped connectivity elements to evaluate the model response. The results show that connected natural fractures redirect hydraulic fractures under low horizontal stress differences, producing deflection angles of 30–50 degrees. When the stress difference exceeds 4 MPa, fracture growth becomes more strongly aligned with the maximum principal stress direction. In the true triaxial tests, the total number of connected natural fractures increased from 14 in the I-shaped network to 17 and 21 in the Y- and X-shaped networks, corresponding to increases of 21.4% and 50.0%, respectively. X-shaped networks showed the strongest sensitivity to stress difference and injection rate, while higher elastic modulus reduced fracture width and promoted longer, narrower fractures. Scale-normalized comparisons based on image-derived experimental measurements showed that the predicted propagation length, fracture width and connected-fracture number followed the experimental trend from I-shaped to Y-shaped and X-shaped networks, with relative errors within 7.1% and a mean absolute percentage error of 4.8%. These findings suggest that fracture topology strongly influences pressure transmission and multidirectional activation in the tested models, whereas field-scale extrapolation requires three-dimensional validation and transport analysis. Full article

Mountain biking over rough terrain exposes riders to vibrations that may affect comfort, health, bicycle control, and performance. This study analyzed the effect of wheel diameter on vibration transmission and performance during a short uphill and downhill test over rocky terrain. Forty-nine highly trained male mountain bikers completed repeated trials using two equivalent hardtail mountain bikes with 26- and 29-inch wheels. Vibrations were recorded with eight triaxial accelerometers placed on the bicycle and rider, and performance was assessed using an electronic photocell timing system. Both wheel sizes showed a similar vibration pattern, with lower root mean square (RMS) acceleration values at the helmet and coccyx and higher values at the wrists and ankles. However, wheel diameter significantly influenced vibration transmission. During the uphill test, the 26-inch bicycle produced higher accelerations at the coccyx and rear hub, whereas during the downhill test, the 29-inch bicycle transmitted greater vibrations to the rider’s wrists and ankles. No significant differences were observed between wheel sizes in the time required to complete either the uphill or downhill tests. These findings suggest that, in short and highly irregular uphill and downhill sections, 29-inch wheels do not necessarily improve performance over 26-inch wheels, although they modify the distribution of vibrations transmitted to the rider. Full article

Light pozzolanic soft clay has high compressibility and relatively poor structural stability, which limits its direct application in subgrade and foundation engineering. This study develops a sustainable combined stabilization–reinforcement system for lightweight volcanic ash soil using a steel slag–fly ash-based composite cementitious binder (GS) and recycled polyester fiber (RPF). Unconfined compressive strength tests, unconsolidated undrained triaxial tests, and microstructural characterization were conducted to evaluate the mechanical behavior and microstructural features of the treated soil. The results show that the GS binder markedly increased the soil strength, whereas RPF mainly improved specimen integrity and the post-peak response. Based on the single-additive and orthogonal test results, 24% GS, 0.6% RPF, and 9 mm fibers were identified as an appropriate mixture within the investigated factor levels for further mechanical evaluation. With the increase in confining pressure, the stress–strain response changes from strain softening to strain hardening. Scanning electron microscopy (SEM) observations showed fine particulate material at local particle-contact and fiber–matrix regions, while energy-dispersive X-ray spectroscopy (EDS) analysis identified a representative Ca-rich microregion containing Si and Al. The combined use of GS binder and RPF effectively improved the strength and deformation resistance of lightweight volcanic ash soft clay. Full article

The exploration of oil and gas resources is shifting toward ultra-deep and extra-deep reservoirs, including in the Tarim Basin, where various types of carbonate rocks are buried. Owing to the extreme burial depths, the mechanical behavior of these rocks under extra-deep conditions differs significantly from that of shallow formations, making it essential to understand their mechanical responses. This study investigated the mechanical properties and failure modes of carbonate rocks, specifically dolomite, argillaceous limestone, and pure limestone. Samples from extra-deep formations were initially analyzed for mineral composition and microstructure, after which uniaxial and triaxial compression tests were conducted to evaluate strength, static elastic modulus, and axial strain at peak stress. The results indicate that dolomite exhibits the highest mechanical strength and stiffness among the three lithologies. Under conditions of a high confining pressure of 100 MPa and a temperature of 160 °C, its elastic modulus and triaxial compressive strength are 65.4 GPa and 611.2 MPa, respectively, compared with 52.8 GPa and 444.2 MPa for limestone. Strength increases with confining pressure for all lithologies, with dolomite showing the most pronounced strengthening response. Although elevated temperature reduces rock strength, its effect is weaker than that of confining pressure. The failure mode is strongly controlled by confining pressure. At low confining pressures, failure is dominated by localized shear bands and brittle fracturing, whereas increasing confining pressure promotes a transition toward quasi-brittle deformation or ductile plastic flow. Dolomite predominantly maintains a quasi-brittle failure mode, argillaceous limestone exhibits a clear brittle-to-ductile transition, and pure limestone shows the greatest tendency to develop ductile plastic flow under high confining pressure conditions. The results further demonstrate that mineral composition and microstructural characteristics play critical roles in controlling the deformation and failure mechanisms of carbonate rocks. High-calcite pure limestone can exhibit ductile-like deformation behavior due to cataclastic processes, allowing significant strain without localization failure. These insights enhance understanding of carbonate rock behavior under extra-deep formations, informing practical applications in geology science. Full article

Understanding the anisotropic mechanical behavior and pore–fracture structure (PFS) evolution of bedded coal under mining disturbance is critical for gas extraction and hazard prevention in deep coal mining. This study employed low-field nuclear magnetic resonance (NMR) and fractal analysis to characterize the PFS of water-saturated coal samples with bedding angles of 0°, 30°, 45°, 60°, and 90°. The pore system was classified into adsorption and seepage pores according to pore size distribution. Real-time triaxial NMR tests were further conducted to reveal the coupled evolution of mechanical responses and PFS under different bedding orientations. Results show that bedding inclination controls pore distribution, connectivity, and structural complexity, while influencing coal strength, deformation, and failure through stress redistribution and bedding-plane activation. The mechanical response and PFS evolution exhibit strong anisotropic coupling during loading. A fractional-order porosity model was established by incorporating bedding orientation, anisotropy, and stress memory based on pore geometry and stress decomposition. Model verification confirms its effectiveness in describing anisotropic porosity and PFS evolution under varying bedding angles. This study provides theoretical support for permeability prediction, stability assessment, and hazard control in deep-bedded coal seams. Full article

Determining the shear strength parameters of granular materials in high waste rock dump slopes is essential for reliable slope stability analysis. In this study, dump materials were sampled from six benches (elevations 2800–2950 m) of an open-pit mine dump slope, and in situ density tests, gradation analyses, and large-scale consolidated drained (CD) triaxial tests were performed. Two PFC2D slope models—one with uniform (spatially averaged) parameters and one with elevation-dependent (layered) parameters—were then established to quantify how spatial heterogeneity affects stability predictions. The results show pronounced vertical heterogeneity: density, porosity, gradation, and shear strength parameters vary systematically among benches, reflecting the combined effects of compaction history and particle segregation during dumping. All specimens exhibited strain hardening and continuous shear contraction, and specimens with a denser, better-graded structure showed higher strength and lower compressibility. The layered model yields a higher factor of safety and shallower, bench-scale slip surfaces, whereas the uniform model underestimates stability and misplaces the critical slip zones. These findings demonstrate that elevation-dependent parameter assignment better represents the heterogeneous failure mechanism of high dump slopes and should be preferred over uniform parameterization in stability analyses of similar waste rock dumps. Full article

Bolted connections in combine-harvester vibrating screens are affected by reciprocating screen motion, frame vibration, and intermittent impact, making weak local vibration components difficult to distinguish from background fluctuations. This study used particle swarm optimization to adaptively select the wavelet basis, decomposition level, and thresholding rule for vibration signal denoising. Triaxial acceleration signals were collected under tightened- and loosened-bolt conditions. Gaussian white noise with input signal-to-noise ratios from 0 to 14 dB was added to evaluate parameter selection under controlled noise levels. The selected wavelet basis and decomposition level varied with the input signal-to-noise ratio. Three or four decomposition levels were selected under stronger noise, whereas two levels were generally sufficient at higher signal-to-noise ratios. Soft thresholding was selected in all tested cases. The optimized method reduced random fluctuations while retaining the main waveform trend in simulated noisy signals. For measured loosened-bolt signals, it reduced background fluctuation and retained local waveform changes. Full article